A TV image or video image includes two interlaced fields of lines, and the time interval which runs between the end of one field and the start of the next, referred to as the field flyback (or vertical flyback), is devoid of video signals. Accordingly, it has been proposed to use this field flyback to send information, for instance “teletext” information. It has been proposed to use these time intervals to send the programs of certain channels as well as to produce an electronic guide to the programs on these channels, known under the acronym EPG for Electronic Program Guide.
This electronic program guide is sent in two parts, SUMMARY and CONTENTS, the SUMMARY identifying each channel by a code CNI (for Country Network Identification) and indicating, for each channel, references or ID numbers identifying blocks of data whose contents relate to the program of the corresponding channel. These ID references are classed in an ascending order and identify, for example in the form of a pair of ID references, the first data block and the last data block allocated to a channel of the SUMMARY. This pair defines a series of identification numbers for each channel.
Presently in France, two channels propose such a guide not only for their own programs, but also for programs of other channels, for instance those in the French language. Such a service could moreover be supplied by each channel for other channels. To supply such a service, the TV set must be equipped with a device which includes a memory storing the information received during the field flyback and concerning the electronic program guide. This memory is then “managed” by programs and algorithms in view of presenting the information according to criteria defined by the viewer, e.g. the programs on a given channel, films shown on the channels at a given date, etc.
It has been determined that the size of the memory needed to record the program of a channel over one week is about 256 kilobytes, i.e. two to three megabytes for around ten channels. This size is without counting the microprocessor memory for processing the information in view of presenting it according to selected criteria. These figures show that the size of the memory limits the service which can be proposed to a TV viewer in that area.